Backward-wave oscillation in traveling wave-tube amplifiers has been a problem since the development of traveling wave tubes in the 1940s. Traveling wave-tube amplifiers are configured to affect interaction between an input radio frequency (RF) wave and an input electron beam. Backward wave oscillation occurs when a reflected RF wave traveling towards the input interacts with the electron beam. The backward wave is amplified and causes oscillation of the traveling wave-tube amplifier. Backward-wave oscillation limits the operational bandwidth of traveling wave-tube amplifiers to a fraction of the theoretical bandwidth as well as its output power.
Various solutions have been attempted to limit the backward-wave oscillation of traveling wave amplifiers. For example, attenuation sections may be added to the traveling wave-tube amplifier to cause attenuation of the backward wave. However, this attenuation also affects the forward wave, and therefore the length of the traveling wave-tube amplifier circuit must be increased to compensate. The lengthening of the traveling wave-tube amplifier creates further backward wave oscillation. Also, from thermal considerations, the attenuations are limited to the traveling wave-tube gain sections and not to the power output section. The existing techniques for limiting backward-wave oscillation still result in loss of bandwidth and provide less efficiency as the power of the input wave is increased.